LEDs are applied in various solutions, for example, LCD backlight and general lighting. LED drivers are needed to supply regulated current to LED strings. Normally, a LED driver may comprise a rectifier and a transformer. The rectifier rectifies an AC signal to a DC signal. The transformer receives the DC signal and provides a converted DC signal having a voltage value decided by the turns ratio of a primary winding of the transformer to a secondary winding of the transformer.
The conventional primary side controlled LED driver may comprise a rectifier, a power switch, a transformer, a secondary circuit, a logic control circuit and a load, e.g. LED strings. In conventional primary side controlled LED drivers, a voltage provided to the LED strings is fixed, so that a current of a LED string is inversely proportional to the number of LEDs in the LED string.
The present disclosure pertains to provide a LED driver providing a constant current to a LED string despite the varying of the number of LEDs in the LED string.